U.S. patent application number 14/162834 was filed with the patent office on 2014-05-22 for surgical prostheses.
This patent application is currently assigned to DePuy International Limited. The applicant listed for this patent is DePuy International Limited. Invention is credited to ALEC BIRKBECK, RYAN COLLINS.
Application Number | 20140142716 14/162834 |
Document ID | / |
Family ID | 40774886 |
Filed Date | 2014-05-22 |
United States Patent
Application |
20140142716 |
Kind Code |
A1 |
BIRKBECK; ALEC ; et
al. |
May 22, 2014 |
SURGICAL PROSTHESES
Abstract
A prosthesis arranged to be coupled to a bone. The prosthesis
comprises a substrate (2) having a surface (6). The surface (6) of
the substrate (2) has a first area and a second area, the first
area being treated such that osseointegration is promoted more than
in the second area. The interface (12) between the first and second
areas forms an alignment mark to assist alignment of the prosthesis
relative to a bone. The prosthesis is arranged to be at least
partially inserted into a bone cavity such that the position of the
alignment mark relative to the bone cavity is indicative of the
angle of insertion of the prosthesis or the alignment mark provides
a position reference for determining the implanted position of the
prosthesis in the cavity. A method of manufacturing the prosthesis
and a method of implanting the prosthesis are also provided.
Inventors: |
BIRKBECK; ALEC; (LEEDS,
GB) ; COLLINS; RYAN; (LEEDS, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DePuy International Limited |
Leeds |
|
GB |
|
|
Assignee: |
DePuy International Limited
Leeds
GB
|
Family ID: |
40774886 |
Appl. No.: |
14/162834 |
Filed: |
January 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13266013 |
Jan 5, 2012 |
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PCT/GB2010/000718 |
Apr 9, 2010 |
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14162834 |
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Current U.S.
Class: |
623/22.21 |
Current CPC
Class: |
A61F 2250/0097 20130101;
A61F 2002/3092 20130101; A61F 2002/30617 20130101; A61F 2/34
20130101; A61F 2002/3093 20130101; A61F 2310/00796 20130101; A61F
2002/30028 20130101; A61F 2/30 20130101; A61F 2/3094 20130101 |
Class at
Publication: |
623/22.21 |
International
Class: |
A61F 2/30 20060101
A61F002/30; A61F 2/34 20060101 A61F002/34 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2009 |
GB |
0907036.8 |
Claims
1-14. (canceled)
15. A method of manufacturing a cup arranged to be inserted into a
bone cavity to form a socket component of a prosthesis ball and
socket joint, the method comprising the steps of: providing a
substrate having a convex surface, a rim and an apex; identifying
at least a first interruption and a second interruption in the
convex surface, the first interruption and the second interruption
extending from the rim and at spaced apart locations at
predetermined angles, the predetermined angles being greater than
zero; and treating at least a first area defined as the area
between the rim and the second interruption and including the apex
to promote osseointegration; treating a second area defined as the
area between the rim and the first interruption to promote
osseointegration to a lesser extent as compared with the treatment
of the first area.
16. The method of claim 15, wherein said step of treating at least
the first area comprises the steps of: masking the interruptions;
and applying a coating to promote osseointegration to the surface
of the first area.
Description
[0001] The present invention relates to surgical prostheses. The
present invention is particular suited to a rotationally
symmetrical surgical prosthesis such as an acetabular cup.
[0002] It is well known to repair bone joints damaged through
disease or injury by implanting prosthetic components to replace
part or all of the natural bone joint. For example, surgical
reconstruction of a hip joint may require a femoral prosthetic
component implanted at the end of the femur to replace the natural
femoral head with a prosthetic bearing head and a prosthetic
acetabular cup implanted within a reamed acetabular cavity or the
natural acetabulum to receive the prosthetic bearing head.
[0003] There are a range of different fixation techniques known for
securing prostheses to the surface of bones, or within bone
cavities. Furthermore, these fixation techniques may be used in
combination. Commonly, mechanical fixation is provided by securing
the prosthesis with screws, pegs, wires or similar fasteners
extending from the prosthesis into the bone. It is also known to
provide a coating to a surface of a prosthesis which when implanted
is in contact with the bone, or in close proximity to the bone,
where the coating is chosen to promote osseointegration.
Osseointegration is the direct structural and functional connection
between living bone and the surface of a prosthesis.
Osseointegration may either result from mechanical retention
whereby bone ingrowth into surface features of a prosthesis, in
particular a metal prosthesis, secures the prosthesis to the bone,
or bioactive retention whereby the implant is coated with a
bioactive material which stimulates bone formation leading to a
chemical bond in which the implant is ankylosed with the bone.
[0004] Osseointegration by mechanical fixation occurs for a number
of metals commonly used within implantable prostheses, such as
titanium and titanium alloys. It can be encouraged by the provision
of topological features like vents, slots and dimples upon the
surface of the prosthesis in contact with the bone. There is no
chemical retention of the prosthesis and the retention is dependent
upon the surface area of the prosthesis.
[0005] Osseointegration by mechanical fixation may be encouraged by
treating a surface portion of a prosthesis to increase its surface
area, for example etching the surface. Alternatively, it is known
to apply a porous coating to the metallic substrate such that bone
ingrowth into the pores forms a firm bond between the prosthesis
and the bone. The porous coating may consist of a plurality of
small discrete particles of a metallic material bonded together at
their points of contact to define a plurality of connected
interstitial pores in the coating. Such a coating material, and a
method of forming the coating, is described in U.S. Pat. No.
3,855,638. Preferably, the particles are of the same metallic
material as the substrate. The coating may be formed by applying an
adhesive to the portions of the substrate to be coated and applying
the particles to the adhesive. Alternatively, a slurry of metallic
powder suspended in an aqueous solution may be formed and applied
to the substrate. The prosthesis is then sintered to remove the
adhesive or aqueous solution and to fuse the particles together and
to the substrate. Such a porous coating is commercially available
from DePuy Orthopaedics, Inc under the name Porocoat.
[0006] Bioactive osseointegration occurs when the coating
stimulates bone formation. A suitable coating material is
hydroxyapatite (HA, also known as hydroxylapatite). Hydroxyapatite
is a naturally occurring mineral form of calcium apatite which
forms up to seventy percent of natural bone. Hydroxyapatite is
commonly used as a filler to replace amputated bone or as a
prosthesis coating to promote osseointegration.
[0007] Correct alignment of an implanted prosthesis relative to the
natural bone, and in particular to any reamed cavity within the
bone arranged to receive the prosthesis, is essential to ensure a
strong bond to the bone and to achieve correct mobility of the
reassembled joint. For instance, for an acetabular cup, a cavity is
formed in the acetabulum (or if appropriate the natural acetabular
cavity may be used) shaped to receive the cup (which generally has
a hemispherical outer surface). The cup is intended to be
positioned eccentrically within the cavity such that a portion of
the cup protrudes above the rim of the cavity. However,
inexperienced surgeons may mistakenly believe that the cup is
intended to be seated and secured in position flush with the
acetabulum rim in order to replicate the cups natural orientation.
This is incorrect and can restrict the movement of the hip.
[0008] A second problem with conventional acetabular cup placement
results from difficulty in positioning the cup owing to the
surgeons viewing angle. To position an acetabular cup, typically
the cup is inserted at an inclination of 40.degree. relative to the
patient's longitudinal axis. It is then typically necessary to
apply 20.degree. of anteversion (rotation about the patient's
longitudinal axis) to assume a correct anatomic position. However,
if the surgeon is viewing the patient on an anterior-posterior
plane then when the operative anteversion is applied the
inclination angle appears to increase. This compound angle effect
could cause an inexperienced surgeon to compensate by reducing the
inclination. However, this results in incorrect cup implantation,
which increases the wear rate of the cup.
[0009] A third problem is that for conventional acetabular cups,
when correctly placed in the cavity portions of the cup protruding
from the cavity may comprise rough surfaces due to surface
treatment of the substrate to promote osseointegration. The rough
surfaces may abrade surrounding soft tissues.
[0010] It is an object of embodiments of the present invention to
obviate or mitigate one or more of the problems associated with the
prior art, whether identified herein or elsewhere. In particular it
is an object of embodiments of the present invention to provide a
prosthesis which aids the surgeon in correctly positioning the
implanted prosthesis by reference to local bone landmarks.
[0011] According to a first aspect of the present invention there
is provided a prosthesis arranged to be coupled to a bone, the
prosthesis comprising a substrate having a surface: wherein the
surface of the substrate has a first area and a second area, the
first area being treated such that osseointegration is promoted
more than in the second area; wherein the interface between the
first and second areas forms an alignment mark to assist alignment
of the prosthesis relative to a bone; and wherein the prosthesis is
arranged to be at least partially inserted into a bone cavity such
that the position of the alignment mark relative to the bone cavity
is indicative of the angle of insertion of the prosthesis or the
alignment mark provides a position reference for determining the
implanted position of the prosthesis in the cavity.
[0012] An advantage of the first aspect of the present invention is
that the alignment mark assists a surgeon in aligning the
prosthesis relative to local bone landmarks. For instance, for
embodiments of the present invention relating to acetabular cups,
the alignment mark may indicate a correct alignment of the cup
relative to the acetabular cavity. More specifically, the alignment
mark may advantageously identify to the surgeon the correct
proportion of the cup to protrude from the bone cavity. This
reduces the risk of a cup incorrectly being inserted flush with the
acetabular rim or the inclination angle being set incorrectly due
to the effect of compound angles from the surgeon's viewing angle.
The surface treatment may comprise applying a coating to the
substrate to promote osseointegration. Alternatively, the surface
treatment may comprise grit blasting the surface or otherwise
treating the surface to remove material to increase the porosity or
surface area of the substrate. The surface treatment may only be
applied to the first area. Alternatively, the first area and the
second area may both be treated, but the amount of treatment or the
type of treatment may vary between the two areas. For instance, the
depth of a coating material may be greater in the first area.
[0013] The position of the alignment mark relative to the bone
cavity may be indicative of the portion of the prosthesis extending
from the cavity.
[0014] The prosthesis may comprise a coating applied to the surface
of the substrate in at least the first area to promote
osseointegration, the second area comprising an interruption in the
coating to form the alignment mark
[0015] According to an embodiment of the present invention there is
provided a prosthesis arranged to be coupled to a bone, the
prosthesis comprising a substrate and a coating applied to a
surface of the substrate to promote osseointegration; wherein at
least one interruption in the coating is provided forming an
alignment mark to assist alignment of the prosthesis relative to a
bone; and wherein the prosthesis is arranged to be at least
partially inserted into a bone cavity such that the position of the
interruption in the coating relative to the bone cavity is
indicative of the angle of insertion of the prosthesis or the
portion of the prosthesis extending from the cavity.
[0016] At least a portion of the coating may be arranged in use to
be in contact with bone tissue. The coating may comprise a porous
coating having a greater surface area than the underlying
substrate. Alternatively, the coating may comprise a bioactive
material to promote bone growth. The interruption in the coating
may be detectable as a difference in roughness of the prosthesis
surface and/or a step discontinuity in the prosthesis surface.
[0017] The prosthesis may be rotationally symmetrical about a first
axis extending into the cavity. In particular, the prosthesis may
comprise a cup arranged to be inserted into a bone cavity to form a
socket component of a prosthetic ball and socket joint. The
interruption in the coating may extend across a portion of a convex
surface of the cup from a rim of the cup to a dividing line
extending across the convex cup surface, the dividing line
extending relative to the rim of the cup at a predetermined angle
such that the interruption in the coating corresponds to a portion
of the cup which is intended to protrude from a bone cavity when
the cup is tilted within the bone cavity. Alternatively, the
interruption in the coating may be formed along at least one line
across the convex surface of the cup extending relative to the rim
of the cup at a predetermined angle.
[0018] According to a second aspect of the present invention there
is provided a method of manufacturing a prosthesis comprising:
providing a substrate; identifying a first area and a second area;
and treating the first area such that osseointegration is promoted
more than in the second area, the interface between the first and
second areas forming an alignment mark to assist alignment of the
prosthesis relative to a bone; wherein the prosthesis is arranged
to be at least partially inserted into a bone cavity such that the
position of the alignment mark relative to the bone cavity is
indicative of the angle of insertion of the prosthesis or the
alignment mark provides a position reference for determining the
implanted position of the prosthesis in the cavity.
[0019] Said step of treating the first area may comprise: masking
the second area of the surface of the substrate; and applying a
coating to promote osseointegration to the surface of the substrate
in the first area such that the coating adheres to the non-masked
first area of the substrate and the masked second area of the
substrate comprises an interruption in the coating forming the
alignment mark.
[0020] According to an embodiment of the present invention there is
provided a method of manufacturing a prosthesis comprising:
providing a substrate; masking a portion of a surface of a
substrate; and applying a coating to promote osseointegration to
the surface of the substrate such that the coating adheres to the
non-masked portions of the substrate and the masked portion
comprises an interruption in the coating forming an alignment mark
to assist alignment of the prosthesis relative to a bone; wherein
the prosthesis is arranged to be at least partially inserted into a
bone cavity such that the position of the interruption in the
coating relative to the bone cavity is indicative of the angle of
insertion of the prosthesis or the portion of the prosthesis
extending from the cavity.
[0021] According to a third aspect of the present invention there
is provided a method of implanting a prosthesis comprising:
inserting a prosthesis into a bone cavity, the prosthesis
comprising a substrate having a surface, wherein the surface of the
substrate has a first area and a second area, the first area being
treated such that osseointegration is promoted more than in the
second area, and wherein the interface between the first and second
areas forms an alignment mark to assist alignment of the prosthesis
relative to a bone; and aligning the alignment mark relative to a
local bone feature by rotating the prosthesis within the bone
cavity such that the position of the alignment mark relative to the
bone cavity is indicative of the angle of insertion of the
prosthesis or the alignment mark provides a position reference for
determining the implanted position of the prosthesis in the
cavity.
[0022] According to an embodiment of the present invention there is
provided a method of implanting a prosthesis comprising: inserting
a prosthesis into a bone cavity, the prosthesis comprising a
substrate and a coating applied to a surface of the substrate to
promote osseointegration, the coating having at least one
interruption forming an alignment mark; and aligning the
interruption in the coating with a local bone feature by rotating
the prosthesis within the bone cavity such that the position of the
interruption in the coating relative to the bone cavity is
indicative of the angle of insertion of the prosthesis or the
portion of the prosthesis extending from the cavity.
[0023] The present invention will now be described, by way of
example only, with reference to the accompanying drawings, in
which:
[0024] FIG. 1 illustrates an acetabular cup in accordance with a
first embodiment of the present invention;
[0025] FIG. 2 illustrates in partial cross section the acetabular
cup of FIG. 1 implanted into a reamed bone cavity; and
[0026] FIG. 3 illustrates an acetabular cup in accordance with a
second embodiment of the present invention.
[0027] Referring first to FIG. 1, this illustrates an acetabular
cup comprising a hollow, generally hemispherical metal substrate 2
and a coating 4 over a portion of the convex surface 6, which when
implanted is at least partially in contact with the bone. The
coating 4 is intended to promote osseointegration and may be a
porous coating such as Porocoat or a bioactive coating such as
hydroxyapatite or any other similar coating material applicable to
a surface of a prosthesis. The cup may have additional bone
fixation means, for instance a screw hole (not shown) generally
positioned at the pole of the hemisphere. The coating 4 extends
over the majority of the convex surface 6, but is interrupted by an
uncoated portion 8 which extends from one edge of the cup rim 10.
The uncoated portion 8 is separated from the coating along a
dividing line 12 which extends along an arc across the convex
surface 6. The arc may begin and end at discrete points about the
rim 10, or may extend to and from a single point on the rim 10.
Alternatively, the dividing line 12 may generally comprise a circle
extending about the cup.
[0028] Referring now to FIG. 2, this illustrates in partial cross
section the cup of FIG. 1 during insertion into a bone cavity 14
formed within a patient's acetabulum. It can be seen that the
dividing line 12 extends across the convex surface 6 at
approximately 20.degree. to the rim 10. The cup is positioned such
that the dividing line 12 is approximately aligned with the
acetabular rim 16 such that the uncoated portion 8 of the cup
protrudes from the reamed acetabular cavity or the natural
acetabulum 14. The angle of the dividing line 12 relative to the
rim 10 is chosen to allow the surgeon to clearly identify the
proportion of the cup which should protrude from the cavity 14. It
will be appreciated that in other embodiments of the invention the
angle between the dividing line 12 and the rim 10 may vary.
[0029] The difference between the coating 4 and the uncoated
portion 8 is clearly identifiable by the surgeon as both a
difference in surface roughness and a step change in the surface of
the cup (equal to the thickness of the coating 4). Consequently the
uncoated portion 8 which serves as an alignment mark for
positioning the cup relative to local bone landmarks (that is, the
acetabular rim 16) is clearly identifiable even if obscured by
blood or other fluids. Clear identification of the alignment marks
is important in ensuring that they are readily identifiable during
surgery. As such, forming alignment marks using differential
coating techniques is preferable to alignment marks formed by laser
marking or applying colours to the prosthesis surface, which may be
more easily obscured.
[0030] The cup may be readily inserted into a prepared cavity by
firstly rotating the cup about its polar axis such that the
uncoated portion points to the edge of the cavity from which the
cup is intended to protrude and then tilting the cup until the
dividing line is parallel to the acetabular rim. As the uncoated
portion of the cup is not in contact with the bone, there is no
loss of strength due to the reduction in the area of the
coating.
[0031] Referring now to FIG. 3, this illustrates an acetabular cup
in accordance with a second embodiment of the present invention.
Features that are common to FIGS. 1 and 2 are referred to using the
same reference numbers. While FIGS. 1 and 2 illustrate a cup
intended to be inserted into a bone cavity such that a fixed
portion of the cup protrudes from the cavity at a fixed angle, it
may be desirable for the angle of protrusion to be chosen by the
surgeon intraoperatively. In place of a single uncoated portion of
the convex surface 6, FIG. 3 illustrates a series of lines 20
within the coating 4 formed from regions where the coating is
absent from the cup. Lines 20 comprise elongate gaps within the
coating such that the coating is present between the lines 20.
There may be four lines 20 as illustrated spaced apart from the rim
10 by 5.degree., 10.degree., 15.degree. and 20.degree., however the
number of lines and their spacing may vary, for instance there may
only be a single line at the same angular position relative to the
rim as the dividing line 12 illustrated in FIG. 1. The lines may
extend to the rim of the cup as shown in FIG. 3, however they may
alternatively stop short of the rim or not intersect the rim.
[0032] Advantageously, if only a limited angular protrusion from
the cavity is required, the reduction of coating area represented
by the lines 20 that are positioned within the bone cavity is
minimal. Conversely, for the cup of FIGS. 1 and 2, if the surgeon
decides to implant the cup at a smaller angular protrusion than
that indicated by the full extent of the uncoated portion then
there may be a significant reduction in coating in contact with the
bone compared with a cup according to the prior art for which the
whole of the convex surface is coated.
[0033] It will be appreciated that in alternative embodiments of
the present invention differing sizes and shapes of the convex
surface may be left uncoated to serve as alignment markings. For
instance, the uncoated lines may be replaced by dashed lines, short
lines not extending fully to the rim or only a single small
circular interruption in the coating. More generally, any
interruption in the coating capable of conveying alignment
information for a prosthesis relative to local bone landmarks is
within the scope of the present invention.
[0034] The interruptions in the coating may be provided by masking
off portions of the prosthesis surface prior to applying the
coating, as will be well known to the skilled person according to
the particular coating material.
[0035] Although the present invention has been described above
primarily with reference to a prosthetic acetabular cup, the
invention is not limited to this application. For instance, the
present invention may be applied to a cup arranged to be couple to
a glenoid of a shoulder joint. More generally, the present
invention is applicable to any prosthetic component and is
particular suited to applications where the prosthetic component
may be implanted at a variable angle relative to the bone, or with
a varying proportion of the prosthesis protruding from a bone
cavity, such that the interruptions in the coating assist in
correctly aligning the prosthetic component. In particular, the
coating interruptions assist in determining the proportion of the
prosthetic component which is intended to protrude from a bone
cavity.
[0036] The interruptions in the coating have been described above
as a difference between a portion of the prosthesis surface where
the coating is applied and a portion of the prosthesis surface
where the coating is absent. However, in alternative embodiments of
the present invention the interruptions may comprise a difference
in coating thickness or the presence or absence of an additional
layer of coating material. In further embodiments of the present
invention there may be no coating material applied to the surface
of the substrate. Instead, selected portions of the substrate may
be treated to promote osseointegration, for instance by increasing
the porosity or surface area of the material. For instance,
selected portions may be grit blasted or otherwise treated to
increase their roughness. The alignment mark comprises the
interface between adjacent surface areas which have been
differently treated to promote osseointegration to different
extents. For instance, one area may not be treated at all, or
treated to a lower extent or treated differently.
[0037] Further modifications to, and applications of, the present
invention will be readily apparent to the appropriately skilled
person without departing from the scope of the appended claims.
* * * * *